Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$242.36	5.790%	$256.3926	$256.39	$256.40	$256.40
Purchase #2	$93.58	13.141%	$105.8773	$105.88	$105.90	$105.90
Purchase #3	$56.27	4.225%	$58.6474	$58.65	$58.65	$58.60
Purchase #4	$5.98	13.179%	$6.7681	$6.77	$6.75	$6.80
Purchase #5	$115.65	3.317%	$119.4861	$119.49	$119.50	$119.50
Purchase #6	$76.88	6.873%	$82.164	$82.16	$82.15	$82.20
Purchase #7	$211.56	4.216%	$220.4794	$220.48	$220.50	$220.50
7 purchase totals =	$802.28		$849.8149	$849.82	$849.85	$849.90